Transcript Design Review - Purdue College of Engineering

ECE 477 Design Review
Team 3 – Spring 2010
Sean Ma Jacob Champion Kelli Hacker George Hadley
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Outline
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Project overview
Project-specific success criteria
Block diagram
Component selection rationale
Packaging design
Schematic and theory of operation
PCB layout
Software design/development status
Project completion timeline
Questions / discussion
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Project Overview
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Arm-wearable device for snowsports enthusiasts
Provides real-time information: current downhill
velocity, temperature, altitude, and airtime - via
headphone audio
“Emergency mode" uses GPS to navigate the
user back to a programmable safe location
Li-polymer battery is monitored and recharged
in-circuit
Target battery life of ten hours
Operational in subfreezing temperatures
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Project-Specific Success Criteria
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An ability to communicate sensor data via audio
to the user
An ability to recharge and monitor an on-board
battery
An ability to determine current location via GPS
An ability to direct the user to a "safe" waypoint
An ability to save acquired data to persistent
storage
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Block Diagram
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Component Selection Rationale
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Major components to be selected:
Audio Interface
 Accelerometer
 Microcontroller
 GPS Module
 Altimeter
 Character LCD
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Component Selection Rationale
Audio Interface: VLSI
VS-1011e
 Streaming WAV and
MP3 decoder
 50 mA active / 30 mA
inactive
 SPI interface (512-byte
packets)
 Headphone driver
Accelerometer: Analog
ADXL345
 40 uA active draw
 SPI interface
 +/-16g maximum
 Free-fall and motion
interrupt support
 Breakout board available
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Component Selection Rationale
Microcontroller: Microchip
PIC24FJ256
 Flexible clock and low
power draw
 Floating-point library
support
 Very few external
peripherals needed
 Large amount of on-chip
Flash and remappable
pins for flexibility
GPS Module: Polstar
PMB-648
 Excellent fix times
 Low power consumption
and configurable update
rates
 Two-wire TTL serial
communication
 Team members have
previous experience
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Component Selection Rationale
Altimeter: VTI
SCP1000-D01
 Incredibly low power
draw (25 uA at 3.3V)
 Up to 9 cm resolution in
ideal conditions
 Onboard thermometer
saves circuit space
 Breakout board
available
 SPI interface operation
Character LCD: Newhaven
NHD-C0216CiZ
 Small, light chip-on-glass
solution
 16 x 2 characters
 Operates on 3.3V
 Bright backlight takes
only 20 mA
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Packaging Design
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Device needs to be wearable
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Device intended to be worn for
outdoor sports
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Lightweight
Small
Durable
Package Choice: OKW ErgoCase
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Fits above criteria
Ergonomic
Designed to be worn on the forearm
Free Samples
Multiple Sizes
Armband included
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Packaging Design
LCD
Pushbuttons
DC Power In
Headphone Jack
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Schematic/Theory of Operation:
Power
Component
Current Consumption
(mA)
Microcontroller
24mA
Accelerometer
40µA
Altimeter
10µA
GPS Module
65mA
LCD Display
20mA backlight, 0.5mA
supply
MicroSD Card
~75mA active
MP3 Decoder
50mA active, 30mA inactive
Total:
234mA (worst case)
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Schematic/Theory of Operation:
Power
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3.3V power rail
provided by LTC3440
buck/boost converter
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On/off slider switch
disconnects regulator
from circuit
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Analog comparator
prevents battery
undervoltage
conditions, shutting
down regulator at
LiPo's minimum 2.75V
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Schematic/Theory of Operation:
Battery
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Battery is charged by a
5V wall wart
connected to an
MCP73811T charge
controller
0.1Ω sense resistor
provides voltage for
LTC4150 fuel gauge
Battery voltage
connected to uC's
ADC for absolute
measurement
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Schematic/Theory of Operation:
Audio
VS1011E
Decodes MP3 files and drives
an audio jack
Manufacturer recommended
circuit
“Native Mode” – recommended
for new projects and easier to
implement
Internal oscillator
Separate digital and analog
grounds
+3.3 V tied to analog and
digital VDD
Audio Circuit
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Schematic/Theory of Operation:
Audio
ESD protection at audio jack
SPI connection to PIC24
SCI for control
SDI to receive data
xDCS chip select for SDI pulled
up – use xCS for both SCI and
SDI
xReset and DREQ also
connected to PIC24
Audio Circuit
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Schematic/Theory of Operation:
Accelerometer
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Analog Devices
ADXL345 Accelerometer
device
Utilizes SPI interface
(shared with Altimeter
module)
Useful features: freefall
detection, interrupt
detection, 13-bit
resolution, ±16g range
Acceleration data
provided used to
determine velocity
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Schematic/Theory of Operation:
Altimeter
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VTI Technologies SCP1000
altimeter device
Utilizes SPI interface (shared
with Accelerometer module)
Useful features: resolution,
18cm accuracy, integrated
thermometer
Derivative of altimeter data
provides Z velocity
measurement (used for slope
detection, velocity
calculations)
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Schematic/Theory of Operation:
GPS Module
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Polstar PMB-648 GPS
module
Utilizes 2-wire TTL Serial
Communication (9600 baud)
Useful features: track up to
20 satellites, enhanced
performance in
canyon/foliage environments
Provides XYZ position
information as well as time,
velocity information used in
slope calculations
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Schematic/Theory of Operation:
Microcontroller
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PIC24FJ256GA106 microcontroller
Central control for Gauntlet device
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Schematic/Theory of Operation:
Microcontroller
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Performs
position/velocity/acceler
ation/time formatting and
calculations
Displays results to user
interface
Monitors power supply
to check for low-battery
conditions
External 8 MHz
oscillator crystal will be
used for increased
UART accuracy w/ GPS
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Schematic/Theory of Operation:
Microcontroller
Microcontroller Interfaces:
 UART: 2-wire TTL 9600 baud serial to GPS
 I2C: 400kHz interface to LCD display
 GPIO:
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Battery Monitor
Battery Charger
Pushbuttons/User Interface
SPI (x3):
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500kHz for shared accelerometer/altimeter interface
3Mhz interface to MP3 Decoder Chip
4MHz interface to SD Card (subject to change)
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Schematic/Theory of Operation:
Storage
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Will be using a microSD card for memory
Cheap, readily available, persistent memory
for prototyping
 Can interface with other devices
 Smaller than normal SD card, so conserves
space
 Will use PIC library for FAT32 File I/O system
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Connect to microcontroller via SPI bus
 No need for pull-ups, according to several
sources
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Schematic/Theory of Operation:
User Interface
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User Input:
Pushbuttons (Use Generic I/O)
 Menu System
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Audio:
The VS1101E MP3 Decoder has built-in audio
driver
 Communicates with microcontroller using SPI
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LCD:
Character LCD
 Communicates via I2C
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PCB Layout
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PCB Layout: Power
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Buck-boost circuit
layout is crucial to
proper
performance
Inductor traces
must be wide to
support high
current
Must be isolated
from other digital
circuitry
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PCB Layout: Battery
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PCB must act as
heatsink for linear
charge regulator
Sense resistor
should be as close
to fuel gauge as
possible
Power traces
should be kept
wide and short for
minimal losses
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PCB Layout: Audio
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Analog and digital ground
need to be tied close to
VS1011E
Decoupling capacitors
placed as near as possible
Header connection for SPI
and microcontroller signals
Audio jack must be on
right edge of PCB for user
access
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PCB Layout: Sensors
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Accelerometer must be by
mounting point to avoid circuit
resonance
Breakout boards for
accelerometer and altimeter
placed on edge of circuit to
conserve space
Accelerometer and altimeter
placed close to one another –
share an SPI bus
Header for ribbon cable to
GPS
Header for access to SPI bus
and chip selects
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PCB Layout: Microcontroller
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64-pin QFP package
Contains 3 digital
power/ground pairs, 1
analog power/ground
pair, Vddcore and
Vddcap pins
Require .01µF
decoupling capacitors
(locate near
microcontroller)
Requires 8MHz
external crystal
(locate near MCU)
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Software Design/Development
Status
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Components verified for correct functionality
Primarily timer-based – allows for low power consumption
At set intervals:
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Poll accelerometer for jump data
Poll GPS and altimeter for velocity and position
Poll altimeter for temperature
Poll battery for absolute voltage
Poll pushbuttons for user input
Act on readings by
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Calculating downhill velocity
Notifying user via audio (user-set intervals)
Saving GPS/altitude waypoints as needed
Activating modes of operation based on user input
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Project Completion Timeline
Week 8
Week 9
Week
10
Week
11
Week
12
Week
13
Week
14
Week
15
1-Mar
8-Mar
22-Mar
29-Mar
5-Apr
12-Apr
19-Apr
26-Apr
Design Review
Start Software
Proof-of-Parts
Final Schematic
Final PCB
Software Design Narrative
All sensor interfaces working in software
Patent Liability Analysis
Put power circuitry on PCB
Reliability and Safety Analysis
Software basically finished
Battery and micro on PCB
Ethical and Enviro Impact Analysis
Software debugging
SD card and sensors on PCB
User Manual
PCB and software finalized
Cut packaging
PSSC Presentation
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Questions?
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